There is a case where a converter device is constituted by a twelve-phase rectification transformer in order to suppress outflow of harmonics to an alternating-current system. There are a case where a twelve-phase rectification transformer is configured with its primary side being made as a Y connection and its secondary side being made as a Δ connection and a Y connection, and another case where a twelve-phase rectification transformer is configured with its primary side being made as a Δ connection and its secondary side being made as a Δ connection and a Y connection. In a twelve-phase rectification transformer, at the secondary side thereof, a three-phase alternating current with a phase difference of 30 degrees is generated and twelve-phase rectification is performed by subjecting the resultant to full-wave rectification (see Patent Literature 1).